Method of using an electrode probe for electronic drier control



Nov. 29, 1966 T. R. SMITH 3,287,817

METHOD OF USING AN ELECTRODE PROBE FOR ELECTRONIC DRIER CONTROL Original Filed April 27, 1962 2 Sheets-Sheet 1 AGENT T. R. SMITH Nov. 29, 1966 METHOD OF USING AN ELECTRODE PROBE FOR ELECTRONIC DRIER CONTROL Original Filed April 2'7, 1962 2 Sheets-Sheet 2 INVENTOR. T/wWm/ Z @mZ/v.

BY yl'lflwm/ m4 AGENT United States Patent 3 287 817 METHOD OF USING A N ELECTRODE PROBE FUR ELECTRONIC DRIER CONTROL Thomas R. Smith, Newton, Iowa, assignor to The Maytag Company, Newton, Iowa, a corporation of Delaware Continuation of application Ser. No. 190,575, Apr. 27,

1962. This application Aug. 4, 1965, Ser. No. 478,531

7 Claims. (Cl. 34--31) This application is a continuation of Serial No. 190,575, filed April 27, 1962, now abandoned, which in turn is a continuation-impart of Serial No. 40,663, filed July 5, 1960, now abandoned and continuing as Serial No. 251,470, filed January 11, 1963, now US. Patent No. 3,197,885, and of Serial No. 22,323, filed April 14, 1960, now abandoned and continuing as Serial No. 329,155, filed December 9, 1963. These related applications are assigned to the same assignee as the present application.

This invention relates to devices for directly determining the condition of (fabrics employed in a control system of a machine for drying fabrics, and more particularly, to electrodes for contacting and completing an electrical circuit through fabrics.

Many attempts have been made to control the termination point of drying operations as related, directly, or indirectly, to the condition of the fabrics. Elberty Patent No. 2,045,381, for example, relies upon the change in conductivity of the fabrics as the moisture is removed in order to discontinue operation of a drying machine at the moment electrical conductivity of the fabrics, as sensed directly between conductors in the drum, attains a predetermined value.

In other control systems, the humidity of the air within the drier is measured to determine when the drying operation should be terminated, instead of direct measurements of the electrical conductivity of the fabrics, illustrated in Horecky Patent No. 2,820,304, for example. Humidity determinations are an unreliable index of the condition of the fabrics, and control systems dependent thereon contain an inherent deficiency.

In still other systems attempts have been made to control the termination of the drying period by thermostats in the drier. In these systems the thermostats operate to shut oil the heaters when the temperature within the drying cabinet rises above a set value which occurs when most of the clothes have been dried. Again, the control does not insure that all of the fabrics have been dried.

Control systems dependent upon the electrical conductivity of the fabrics react to the instantaneous conditions. Consequently, a heavy fabric may dry on the outside more rapidly than on the inside, so that there is a premature indication of dryness.

It is an object of the present invention to provide a control method for a clothes drier responsive to the dry condition of the fabrics being treated. It is a further object of the invention to provide a method for controlling termination of a drying operation that is responsive to the direct determination of the electrical conductivity of the fabrics, so as to obtain reliable shut-01f of the drying operation. It is a still further object of the invention to provide a method whereby direct response of the control to the dryness or conductivity of fabrics is made practical or feasible for home laundry clothes driers. Further objects and advantages of this invention Will become evident as the description proceeds and from an examination of the accompanying drawings which illustrate several embodiments of the invention and in which similar numerals refer to similar parts throughout the several views.

In the drawings:

FIGURE 1 is a view in vertical section, partly broken away showing a drier which incorporates the control system of the invention;

33,287,817 Patented Nov. 29, 1966 FIGURE 2 is an enlarged view in longitudinal section of one of the baffles in the drum, illustrating the arrangement of electrodes there-on;

FIGURE 3 is a top plan view of the bafiie shown in FIGURE 2;

FIGURE 4 is a bottom view of the baffle shown in FIGURE 2;

FIGURE 5 is an end view of the lbaflie shown in FIGURE 2;

FIGURE 6 is an enlarged view in section taken substantially along lines 66 of FIGURE 4;

FIGURE 7 is an enlarged view in section taken substantially along line 77 of FIGURE 4.

Briefly described, the invention relates to a control system for termination of the drying operation in which conductors, electrodes, or probes, directly contact fabrics being dried to directly determine their electrical conduc tivity. The conductors, electrodes, or probes, which are mounted in a revoluble drum, contact water absorptive material for preventing premature termination of the drying operation.

Referring now to the drawings, FIGURE 1 shows a clothes drier having a base frame 10 which serves as a support for upstanding channel base members 11 and 12 which together with cross piece 14 support the hollow blower housing casting 17. Housing 17 includes a tubular portion 21, a divider wall 20 having a rearwardly flared inner portion defining an intake into an impeller chamber, and radially directed longitudinal webs 22 which converge toward each other to provide a retainer member 23. A passageway 26 is located between the tubular portion 21 and the bearing retainer member 23 which transverses the supporting webs 22.

Within member 23 is journalled a revoluble drum drive shaft 31 which projects from both ends of the housing 17. Aflixed to drum drive shaft 31 at the rear of the cabinet is a large pulley 33 which is driven by motor 34 through motor pulley 36, main drive belt 37, a speed reduction system (not shown) and belt The opposite or forward end of the drum drive shaft 31 is rigidly connected to the drum spider member 46 which has radiating spokes 51 that support rim 52. A heat resistant sealing member 54 encircles the front pe riphery of blower housing 17 and the circular shoulder 55 located on the rear portion of drum spider 46.

A horizontally mounted tumbling drum has a rear wall 61 which is secured to rim 52 for support and rotation by shaft 31. Rear drum wall 61 is imperforate except for a central exhaust opening 62.

The periphery of rear wall 61 is flanged to form a. supporting shoulder for the imperfo-rate cylindrical side wall 65 which carries the clothes elevating vanes 66 for tumbling clothing within drum 60' during rotation of the latter member. Cylindrical side wall 65 is connected to the front drum wall 67.

Front wall 67 has a centrally located access opening 68 and a circular perforate portion 69 located concentrically to access opening 68. This perforate portion 69, formed by several concentric rows of holes, serves as the air intake into drum 60.

The cabinet 70 which is fastened to base frame 10 and which encloses the entire drying mechanism has an access opening 71 aligned to drum access opening 68 thereby allowing both of openings 68 and 71 to receive the door gasket 72. The door 73 is hinged to form with gasket 72 an airtight seal for cabinet 70.

Fastening to cabinet 70 is the shroud or cowling member 74. Located between shroud 74 and the front drum wall 67 is an open coil electric heating element 75 which extends completely around the inside of cowling member 74 to raise the temperature of air passing through perforate portion 69 in the front drum wall 67. It will be understood that a gas heater may be used in place of the electrical element.

Air flow into drum 60 through the perforate area 69 and into the blower housing 17 is produced by rotation of the revoluble impeller member 76 located in blower housing 17. Fan pulley 77 is connected to the driving motor 34 by main drive belt 37. The blower housing casting 17 supports a cycling thermostat 78 which is connected in series with the heating element 75 in order to maintain the interior of drum 60 at the pro-per selected drying temperature.

In order to measure the electrical conductivity or resistance for determining the condition of dryness of the fabrics, electrodes or probes 80, 81 are mounted within the drum 60. In the form shown, a pair of electrodes of opposite polarity are mounted on the drum baffles 66 to provide a maximum amount of contacting or probing surfaces exposed to the fabrics placed within the drum. The electrodes may be mounted very close together, for example from inch to /s inch apart, so that fabrics falling on both electrodes in a pair simultaneously, will, through their varying resistance, operate the electrical control system in control unit 92.

As best illustrated in FIGURES 2, 3, 5, 6, and 7, a Water absorptive material 82 contacts both electrodes 80, 81 in order to form an electrical circuit therebetween of relatively low, or high, electrical resistance when the material is wet, or dry, respectively. The water absorptive material is positioned on the baffle so as to absorb moisture from the tumbled fabrics. In operation, the wet fabrics will transfer moisture to the material 82 and a condition of equilibrium will be established between the material 82 and the interior of the heavy fabrics. The moisture equilibrium between the material 82 and the fabrics tends to maintain a moisture content of the material 82 corresponding to the interior of .the heavy fabrics, so that the material 82 and the interior of the heavy fabrics will dry somewhat about the same time. By keeping the moisture content of the material 82 corresponding to the interior of the fabrics, premature shutoff of the drying operation will be reduced.

Although the material 82, as illustrated, is mounted on baffles 66, it will be realized that it may be located anywhere, even outside drum 60, as long as it can establish and maintain a moisture equilibrium with the fabrics. In some instances it may be desirable to have the material 82 spaced from the tumbled load.

The water absorptive material must possess relatively high electrical resistance when dry and be able to hold moisture so as to set up a moisture equilibrium with the fabrics. Suitable materials include wood, cloth, paper, ceramic, plastic and the like. Porous materials with high electrical resistance when dry have been found useful. Water insoluble hygroscopic materials also may be used. It is to be understood that all materials are not equally desirable and some will be more preferable than others.

Electrical energy is supplied to electrode 80 by lead 84 that is connected to brush 85 which engages the stationary slip ring 86 while the drum 60 is rotating. The slip ring 86 may be supported on an electrically insulative band 87 mounted on housing 17. Slip ring 86 is in turn connected .to a lead 90 which runs to the control unit 92. Electrode 81 may also be supplied with electrical energy of the opposite polarity to electrode 80 by similar arrangement of brushes and slip rings. It is preferred, however, to ground electrode 81 to the rotatable drum 60, so that it is supplied by current from lead 91 which is also grounded to the framework of the drier.

The automatic control unit 92 may be secured .to the upper portion of the cabinet. Leads 90, 91 enter the control unit and are connected to the control circuit to be described hereinafter.

Bafiiles 66 may be conveniently formed of electrically non-conductive material in order to insulate the eleci trodes from the drum. However, the electrodes are electrically shorted by contacting the wet fabrics during tumbling.

Ordinarily, a plurality of baffles 66 are mounted within the drum 60, each of which is provided with electrodes 80, 81, and the respective electrodes of all the baffles connected electrically in parallel, although a single bafile provided with electrodes may be used.

The baffles may be hollow to reduce the expense and weight. Screw sockets 99 are formed in the base of the baffles for mounting to the interior surface of the drum.

Referring now to FIGURES 2 through 7, which illustrate the bafiies in detail, the electrodes 80, 81 are mounted on the inner edge, or crown, of the bafiies. As best shown in FIGURE 4, electrodes and 81 are connected .to the baflles by bolts 97, 93, and 98, 94, 96, respectively, which project into the hollow interior of the bafiles. The leads 83 and 84 are electrically connected to the control system and to electrodes through bolts 96 and 95 respectively.

Since the electrodes operate the control system in response to fabric electrical conductivity, it is undesirable that the surface condition of thick, or heavy, fabrics be the only condition sensed :by the electrodes. By positioning water absorptive material 82 across electrodes a moisture equilibrium is established through which the material 82 tends to follow the moisture content of the entire fabric even though the fabric may be susceptible to drying more rapidly on the surface. The result is that the electrodes respond to the moisture content of the material 82, as well as surface of the fabrics. In this way, premature termination of the drying operation is largely avoided for heavy fabrics, such as bath sets, Turkish towels, and the like. The termination procedure in a control system of this nature is set forth in the hereinabove mentioned Serial No. 22,323 filed April 14, 1960, with a foreign counterpart thereof having issued in France as Patent No. 1,269,901 dated September 5, 1960. The magazine Appliance Manufacturer on page 27 of its January, 1962, issue also describes the termination procedure followed in response to predetermined electrical conductivity between electrodes. Briefly, upon reaching the predetermined conductivity value, the control system shuts off the beat supply to the drum 60 but continues rotation of the drum 60 and impeller member 76 for a short period to reduce the drum temperature before complete shutdown of the clothes drier is effected.

In the drawings and specification there have been set forth several embodiments of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for purposes of limitation. Changes in form and the proportion of parts, as well as the substitution of equivalents are contemplated, as circumstances may suggest or render expedient, without departing from the spirit or scope of this invention as further defined in the following claims.

I claim:

1. In the drying of wet fabrics the method of control ling termination of the drying operation comprising: effecting contact between said fabrics and water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp electrically connected across a pair of spaced electrodes,

establishing a degree of moisture equilibrium by direct contact between said fabrics and said absorptive material sothat as the drying operation proceeds the moisture content of the absorptive material tends to follow the moisture content of the fabrics being dried, determining the electrical resistance between said electrodes, maintaining said fabric drying operation until the electrical resistance between said electrodes reaches a predetermined value,.

and initiating termination of said drying operation responsive to the sensing of said predetermined value of resistance.

ling termination of the drying operation comprising: effecting contact of said fabrics with a pair of spaced electrodes and with a water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp extending between said electrodes, establishing a degree of moisture equilibrium by direct contact between said fabrics and said absorptive material so that as the drying operation proceeds the moisture content of the absorptive material tends to follow the moisture content of the fabrics being dried, determining the electrical resistance of the fabrics contacting said electrodes, maintaining said fabric drying operation until the electrical resistance between said electrodes reaches a predetermined value, and initiating termination of said drying operation responsive to the sensing of said predetermined value of resistance.

3. In the drying of wet fabrics the method of controlling termination of the drying operation comprising: effecting contact between said fabrics and a pair of spaced electrodes for determining electrical resistance of the fabrics contacting said electrodes, effecting direct contact between said fabrics and a water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp extending between said electrodes, maintaining said fabric drying operation until the electrical resistance of the fabrics and absorptive material between said electrodes reaches a predetermined value to prevent premature termination of the drying operation, and interrupting said drying operation responsive to the sensing of said predetermined value of resistance for terminating the drying operation.

4. In the drying of wet fabrics the method of controlling termination of the drying operation comprising: effecting random contact of said fabrics with a pair of spaced electrodes .and with a water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp electrically bridging said electrodes, establishing a degree of moisture equilibrium by direct contact between said fabrics and said absorptive material so that as the drying operation proceeds the moisture content of the absorptive materials tends to follow the moisture content of the heavier fabrics being dried, determining the electrical resistance between said electrodes, maintaining said fabric drying operation until the electrical resistance of said absorptive material between said electrodes reaches a predetermined value to prevent premature termination of the drying operation with loads containing heavy fabrics, and initiating termination of said drying operation responsive to the sensing of said predetermined value of resistance.

5. In the drying of wet fabrics the method of controlling termination of the drying operation comprising: effecting contact of said fabrics with a pair of spaced electrodes and with a water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp extending between said electrodes, establishing a degreeof moisture equilibrium between said fabrics and said absorptive material through the direct contact of said fabrics with said absorptive material so that as the drying operation proceeds the moisture content of the absorptive material tends to follow the moisture content of the fabrics being dried, determining the electrical resistance of the fabrics and absorptive material contacting said electrodes to sense the presence of moisture, maintaining said fabric drying operation until the electrical resistance of the fabrics and absorptive material between said electrodes reaches a predetermined value, and initiating termination of said drying operation responsive to the sensing of said predetermined value of resistance.

6. In the drying of wet fabrics the method of controlling termination of the drying operation comprising: moving said fabrics to effect contact with a pair of spaced electrodes and with a water absorptive material having a high electrical resistance when dry and a relatively lower electrical resistance when damp electrically bridging said electrodes, establishing a degree of moisture equilibrium by direct contact between said fabrics and said absorptive material so that as the drying operation proceeds the moisture content of the absorptive material tends to follow the moisture content of the fabrics being dried, determining the electrical resistance between said electrodes, maintaining said fabric drying operation ineluding the application of heat and the moving of said fabrics until the electrical resistance between said electrodes reaches a predetermined value, and interrupting said application of heat and then interrupting the moving of said fabrics to terminate said drying operation responsive to the sensing of said predetermined value of resistance.

7. In the drying of wet fabrics in a revoluble container the method of controlling termination of the drying operation comprising: tumbling said fabrics in said rotatable container to effect random contact of said fabrics with a pair of spaced electrodes positioned in said container and connected to an electronic control for determining relative moisture content of said fabrics by measuring electrical resistance through the fabrics contacting said electrodes and further to effect direct random contact of said fabrics with a water absorptive material disposed between said electrodes for transferring moisture directly between said fabrics and said material for establishing and maintaining a degree of moisture equilibrium therebetween to electrically short said electrodes when damp .and electrically separate said electrodes when dry, maintaining said fabrics tumbling with heat applied until the electrical resistance of the fabrics and the absorptive material between said electrodes reaches a predetermined value, interrupting said heating responsive to sensing of said predetermined value of resistance by said electronic control while maintaining said tumbling for a predetermined period of time and then interrupting said tumbling to terminate said drying operation.

References Cited by the Examiner UNITED STATES PATENTS 7/1959 Reiley 3445 7/1961 Woodl-ing 3445 X 

1. IN THE DRYING OF WET FABRICS THE METHOD OF CONTROLLING TERMINATION OF THE DRYING OPERATION COMPRISING: EFFECTING CONTACT BETWEEN SAID FABRICS AND WATER ABSORPTIVE MATERIAL HAVING A HIGH ELECTRICAL RESISTANCE WHEN DRY AND A RELATIVELY LOWER ELECTRICAL RESISTANCE WHEN DAMP ELECTRICALLY CONNECTED ACROSS A PAIR OF SPACED ELECTRODES, ESTABLISHING A DEGREE OF MOISTURE EQUILIBRIUM BY DIRECT CONTACT BETWEEN SAID FABRICS AND SAID ABSORPTIVE MATERIAL SOTHAT AS THE DRYING OPERATION PROCEEDS THE MOISTURE CONTENT OF THE ABSORPTIVE MATERIAL TENDS TO FOLLOW THE MOISTURE CONTENT OF THE FABRICS BEING DRIED, DETERMINING THE ELECTRICAL RESISTANCE BETWEEN SAID ELECTRODES, MAINTAINING SAID FABRIC DRYING OPERATION UNTIL THE ELECTRICAL RESISTANCE BETWEEN SAID ELECTRODES REACHES A PREDETERMINED VALUE, AND INITIATING TERMINATING OF SAID DRYING OPERATION RESPONSIVE TO THE SENSING OF SAID PREDETERMINED VALUE OF RESISTANCE. 